Flight Question unable to launch properly

[stargatechev]

Ok I'm a Novice and yes i've read the tutorials but can't seem to find the right angle of acent! So this is the problem: I launch atlantis for a ISS docking mission but it always seems i'm off inclination to ISS by at least + or -40 degrees no matter what angle rollover or heading I position at launch.

I use the launch MFD and the compass but every heading i try to achieve always heads way off the iss inc. I assume at launch, shuttle rollover 180 degrees then pitch back to heading 80 degrees or maybe not? I try to launch behind the ISS so i can catch up with it...assuming that is right!

If not please do help me, i'm literally grounded!

 

[garyw]

I use the launch MFD and the compass but every heading i try to achieve always heads way off the iss inc. I assume at launch, shuttle rollover 180 degrees then pitch back to heading 80 degrees or maybe not? I try to launch behind the ISS so i can catch up with it...assuming that is right!

In a word.... no, sorry!

First of all, don't think of the ISS as ahead or behind. In space it's all relative.
What you need to do is launch when the yellow line of the ISS path intersects your launch site. Launch MFD will tell you the exact moment this happens.

Second, the shuttles 180 rollover doesnt change the plane. It just goes from being 'upside down' to 'right side' up.

Thirdly, The heading in degress for the ISS from KSC is 42.5 so I'm not sure where you got 80 from. That's way too shallow to get you into the right inclination. Launch MFD will also give you this heading. In real life the shuttle only launches on the AN (Ascending Node) to the ISS.

Finally, try the delta-glider first. It's a lot more forgiving than the shuttle. There are also some excellent tutorials Tex has put togther and there is Bruce Irvings go play in space.

All provide wonderful tips for the novice and even the experienced.

 

[stargatechev]

Thanks for your help will give it another try!

In a word.... no, sorry!

First of all, don't think of the ISS as ahead or behind. In space it's all relative.
What you need to do is launch when the yellow line of the ISS path intersects your launch site. Launch MFD will tell you the exact moment this happens.

Second, the shuttles 180 rollover doesnt change the plane. It just goes from being 'upside down' to 'right side' up.

Thirdly, The heading in degress for the ISS from KSC is 42.5 so I'm not sure where you got 80 from. That's way too shallow to get you into the right inclination. Launch MFD will also give you this heading. In real life the shuttle only launches on the AN (Ascending Node) to the ISS.

Finally, try the delta-glider first. It's a lot more forgiving than the shuttle. There are also some excellent tutorials Tex has put togther and there is Bruce Irvings go play in space.

All provide wonderful tips for the novice and even the experienced.

 

[blixel]

I like to take notes as I learn different things about Orbiter. I know there is no way I'm going to remember everything when I take a few weeks or a few months between flights. I write notes purely for myself, but I tend to write them as if I'm speaking to other people.

Anyway, here are the notes I've taken for myself to rendezvous with the ISS. It's long, so you may not be interested.

Also, I don't go into any detail about the final docking procedure as I've never had any trouble with that part. My difficulty was just figuring out how to rendezvous with the ISS in the first place. Once I actually catch up to the ISS and cancel out the relative velocity, I find the actual docking process relatively easy. (Time consuming, but easy.)

If anyone reads this and wants to offer any corrections, I'd appreciate it. I haven't taken the time to clean it up and format it nicely yet. I'll get to that some day.

 

[Adelanthal]

If you don't mind some math, here's a procedure to get the proper heading (azimuth):

Abbreviations used:
LL : Launch Latitude - Get this from Surface MFD, if your latitude is south of the equator, use the negative of your latitude (20S = -20)
DOI : Desired Orbital Inclination - Get this from Orbit MFD; select your target and read off its Inclination, but make sure that you're in EQU mode
FOV: Final Orbital Velocity - Get this from Orbit MFD (Vel), make sure this is in m/s, not km/s
SOE: Speed on Earth - Again from Orbit MFD (your Vel)

Rough Launch Azimuth:
arcsin ( cos (DOI) / cos ( LL) )

True Launch Azimuth (useful when launching from away from the equator):
arctan ( tan (Rough Launch Azimuth) - SOE / ( FOV * cos (Rough Launch Azimuth) ) )

As an example, launching from KSC to ISS:
LL = 28.59N = 28.59
DOI = 51.57
FOV = 7699
SOE = 407.9

Rough Launch Azimuth = arcsin ( cos (51.57) / cos (28.59) )
= arcsin ( .6216 / .8781)
= arcsin ( .7079 ) = 45 degrees

True Laucnh Azimuth = arctan (tan ( 45) - 407.9 / ( 7699 * cos ( 45 ) ) )
= arctan ( 1 - 407.9 / (7699 * .7071)
= arctan ( 1 - 407.9 / 5444)
= arctan ( 1 - .07493)
= arctan (.92507) = 42.8 degrees

 

[Mister Mxyzptlk]

As GaryW said you really need to learn the Delta Glider first. starting out wit the Shuttle will just be frustrating and discouraging.

 

[stargatechev]

I've tried the DG4 and resulted in the same problem "way off the orbital plane with the ISS"
I took off from KSC on a heading of 42 degrees but the MFD showed me the orbital plane off rinc by at least 70 degress. the problem.. well on the runway ISS is positioned at somewhere around 166W 38N....so you see the problem now...i did everything according to the tutorial but if i head 42 degrees to the ISS it won't work!

The video tutorial shows the ISS moving in a NorthEast direction ..but on mine its heading SouthEast at 166W 38N.

 

[orb]

I've tried the DG4 and resulted in the same problem "way off the orbital plane with the ISS"
I took off from KSC on a heading of 42 degrees but the MFD showed me the orbital plane off rinc by at least 70 degress. the problem.. well on the runway ISS is positioned at somewhere around 166W 38N....so you see the problem now...i did everything according to the tutorial but if i head 42 degrees to the ISS it won't work!

The video tutorial shows the ISS moving in a NorthEast direction ..but on mine its heading SouthEast at 166W 38N.

You need either to wait for the time when ISS will be ascending / moving in a North-East direction / toward descending node, or launch with 138 degrees heading (from KSC) at that time when ISS is moving South-East.

But if you follow a tutorial which tells you to launch with 42 degrees heading, wait for the time when the ISS will be moving in North-East direction.

 

[Urwumpe]

Yes, you need two angles for describing the orientation of the orbit plane in space.

The angle between equator (EQU) or ecliptic (ECL) is inclination. You can control your inclination by your launch azimuth, but the minimum equatorial inclination you can get without dog-leg maneuver is the latitude of your launch site (North or South). More is always possible, less not.

The next angle is the "longitude of the ascending node" (LAN). It describes where your orbit ground track crosses the equator (or ecliptic plane, if used) from South to North at a defined time in history, this time is called epoch. The Epoch that Orbiter uses is J2000 or 1.1.2000, 12:00 GMT. Thus, as you can imagine now, your LAN will change depending on how much Earth did rotate since then.

For getting the same LAN and Inclination as the ISS, which then means you are orbiting in the same plane as the ISS, you need to launch at the right time (which the orbit plane of the ISS crosses your launch site) into the right direction (the direction in which the ISS would be traveling, if it would be right above your launch site). Easy, isn't it?

From KSC, because of legal implications, you can't launch to the ISS when it is travelling from North to South - you would cross Cuban airspace then, and the Cubans are touchy there... but in Orbiter that doesn't really matter much.

You just need to remember: Your azimuth has to change then. Approximately to 180° - 42° = 138°. In practical flight, you also need to include the rotation speed of Earth in the calculation, that is what launch MFD does for you. Otherwise, you would need to enjoy pretty complex vector math.